As illustrated in FIG. 1, a process has long been used to produce glass filaments 6 by introducing molten glass into a bushing 1, drawing the molten glass through numerous nozzles 2 arranged on the bushing 1, cooling the resulting filaments of the molten glass, and then gathering and taking up the thus-formed glass filaments on a winding roll 7.
As a method for effecting the cooling, it is known to arrange cooled fins 3 in proximity with the numerous nozzles 2 arranged on the bushing 1 such that the filaments of the high-temperature molten glass are solidified shortly after their melt-spinning through the nozzles 2. As shown in FIG. 7, for example, JP-B-06053591 discloses a method that coolant is introduced through an inlet port of a header (manifold) 4, is caused to pass through the header 4, and is then discharged through an outlet port 10.
With the method disclosed in the above-cited patent publication, however, the coolant, as shown in FIG. 7, is introduced through the inlet port 9 arranged at a single position of the manifold 4 and, after the coolant is caused to pass through a hollow section of the manifold 4 and hence to flow in a direction through the hollow section of the manifold 4, the coolant is discharged through the outlet port 10. As the fins 3 and manifold 4 have been rendered hot by heat from the bushing 1, the temperature of the coolant tends to rise until it reaches the outlet port 10. A difference is, therefore, developed in temperature between the coolant at the inlet port 9 and that around the outlet port 10. Due to this temperature difference and other causes, the fins 3 joined to the manifold 4 tend to become uneven in temperature and hence, are accompanied by problems such that the fins may undergo deteriorations by separation of an anti-corrosive plating applied to the fins 3 and the fins 3 may become uneven in cooling capacity to make the temperature profile of the bushing 1 uneven.
The following measures may be contemplated to overcome the above-described problems.
(1) By increasing the flow rate of coolant to have more heat absorbed by the fins 3, the temperature difference between the inlet port 9 and the outlet port 10 can be decreased. There is, however, a limitation to the flow rate of coolant which can be allowed to flow in a direction so that deteriorations of the fin 3 still cannot be avoided. Accordingly, the temperature profile of the bushing 1 becomes uneven, and the resulting glass filaments involve problems such that they vary in diameter, are prone to breakage, and may be lowered in production yield. To increase the flow rate of coolant in a direction, it is necessary to increase the diameter of the hollow section of the manifold 4. This naturally necessitates making the manifold 4 bigger, leading to problems in that a higher material cost is required and the convenience of assembly such as attachment is lowered.
(2) By lowering the temperature of coolant, a relatively efficient cooling effect can be obtained because the temperature of the coolant remains low throughout the hollow section of the manifold 4, although a temperature difference still occurs between the inlet port 9 and the outlet port 10. This measure, however, requires a cooling apparatus, and is accompanied by problems such that a higher initial cost is required and more complex production facilities are needed.
(2) By lowering the temperature of coolant, a relatively efficient cooling effect can be obtained because the temperature of the coolant remains low throughout the hollow section of the manifold 4, although a temperature difference still occurs between the inlet port 9 and the outlet port 10. This measure, however, requires a cooling apparatus, and is accompanied by problems that a higher initial cost is required and more complex production facilities are needed.
(3) By increasing the thickness of the fins 3, the progress of their corrosion can be retarded. This measure, however, involves a problem that the machinability of the fins, such as angle adjustability of the fins 3 in a gathering direction of filaments, is reduced.
(4) By decreasing the length of the fins 3, the progress of their corrosion can also be retarded. Heat absorption, however, is proportional to the length of the fins 3, so that the number of nozzles 2 which can be arranged must be determined depending upon the length of the fins 3. Therefore, the use of shorter fins leads to a need for decreasing the number of nozzles 2, and is not preferred.
(5) If the manifold 4 is divided to provide the bushing 1 with many manifolds 4, a relatively efficient cooling effect can be brought about. This measure, however, involves problems in that a higher initial cost is required and more complex production facilities are needed. Further, use of many manifolds 4 requires to leave spaces between individual manifold-fins units. This, however, naturally requires a reduction in the number of nozzles, leading to a problem that the efficiency of production of glass filaments is lowered.
With the above-described problems in view, the present invention, therefore, has as a primary object the provision of an apparatus for producing continuous glass filaments, which without using a complex construction, can provide fins with improved durability, can produce glass filaments with improved quality, and can be applied especially to a large bushing having many nozzles.